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2.  Air Cleaner
A.  The air cleaner is an in-line inertial type. Air leaving the engine heat exchanger (precooler) is ducted into the center of the air cleaner, which is lined with louvered vanes around the perimeter. The air passing through the cleaner is forced to change direction abruptly, to pass through the louvers. This tends to force any heavy particles suspended in the air to continue on to the downstream end of the cleaner where they are collected in a collector ring. The collector ring is connected by the purge air duct through the purge valve to the ram air exhaust duct downstream of the turbofan valve. An air cleaner nozzle in the connection to the ram air exhaust duct limits the amount of air vented overboard for purging the air cleaner. When the purge valve is open air is bled through the collector ring, blowing the particles into the purge air duct and overboard. The clean air is ducted around the outside of the collector ring and into the pneumatic manifold. (See figure 2.)
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Jul 15/70  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  21-12-0 Page 1 

H18580
Air Cleaner System Components Location  501 
21-12-0  Figure 1  May 15/70 
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

3.  Purge Valve
A.  The purge valve is a pneumatically operated, electrically controlled, butterfly valve which controls the flow of bleed air from the air cleaner collector ring. The valve consists of an actuator and butterfly assembly and a solenoid operated pilot valve assembly.
B.  The actuator is divided into two pressure chambers, an opening chamber and a closing chamber, by a diaphragm assembly. The opening chamber is ported to the solenoid pilot valve, and the closing chamber is vented to ambient. The diaphragm actuates the butterfly through a connecting rod and linkage, and is spring loaded in the valve closed position. The butterfly valve consists of a butterfly disk which seats against a floating type seal located within the airflow duct of the valve body. The butterfly shaft has an external valve position indicator and the linkage has an adjustment screw for port leakage adjustment.
C.  The solenoid operated pilot valve consists of a solenoid and a three port, two position poppet valve. One port is connected to the downstream side of the turbofan valve to sense pneumatic duct pressure. The second port is vented to ambient and the third port is connected to the actuator opening chamber. When the solenoid is de-energized the poppet connects the opening chamber to ambient, and closes off the port to duct pressure. When the solenoid is energized the poppet connects the opening chamber to duct pressure and closes off the ambient port. Energizing of the valve solenoid will actuate the valve to the open position as long as the pneumatic duct pressure exceeds ambient by more than the force of the valve closing spring (5 psi).
4.  Electrical Control
A.  Power to the purge valve solenoids is supplied from the 28-volt dc TURBOFAN VALVE circuit breaker on the P6 circuit breaker panel, through the pack valve closed relay and turbofan control relay. The circuit to the purge valve is completed through the APU BLEED switch contacts on P5 panel. (See figure 2.)
5.  Operation
A.  The air cleaner system is completely automatic in operation. The air cleaner purge valve for engine No. 1 or No. 2 is opened whenever the air conditioning system is operating, the APU bleed switch is off, and the airplane is on the ground (landing gear safety relay energized) or the flaps are extended (mach trim switch closed). The air cleaner purge valve will automatically close whenever the air conditioning system is off, APU bleed switch is on, or during flight after flaps have been fully retracted.
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May 01/75  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  21-12-0 Page 3 

Air Cleaner System Schematic  501 
21-12-0  Figure 2  May 15/72 
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

AIR CLEANER SYSTEM - ADJUSTMENT/TEST
1.  General
A.  The air cleaner system does not require adjustment as the amount of bleed air required to purge the cleaner is predetermined by the air cleaner nozzle assembly in the ram air exit duct.
B.  Testing the air cleaner system consists of checking the proper functioning of the electrically controlled pneumatic purge valve. The test is effective in establishing the correct function of the electrical control circuit and the operation of the surge valve.
C.  The test is accomplished separately for each system with the respective air conditioning system operating, pneumatic system pressurized and electrical power provided to the airplane. The following test is applicable to either right or left air cleaner system.
　
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